1. Field of the Invention
The present invention relates, in general, to image scanning, and in particular, to production of an electronic version of a scanned optical image.
2. Description of the Prior Art
It is often desired to scan an image of a target and then convert that image into an electrical signal for subsequent processing and viewing. Airborne scanners are well-known in which a slit is placed in front of a charge-coupled device ("CCD") array in a camera and the moving aircraft then sweeps (scans) the slit past the ground-based image target in a so-called "push-broom" mode, thereby causing the large ground-based image to be scanned as the aircraft flies over the ground. Such scanners have the disadvantage that the airborne scanner platform must move with respect to the target in order to accomplish the scanning.
Other image scanning devices, such as flatbed scanners or drum scanners, are known in which the target image is moved past a scanning head so that the image can pass through optics and into a camera and/or onto a CCD array.
In all such prior art devices, either the (one-dimensional or two-dimensional) CCD array must be large enough to receive the entire image at once or else the scanning process must move the target relative to the scanner so that the entire image can be scanned, and, in all such known devices in which the target moves relative to the scanner, the CCD array remains fixed (non-moving) with respect to the front objective lens of the scanner.
It is also desirable to be able to obtain a spectral representation or imaging spectrograph of the frequency components of an image so that the spectral representation may be further processed to reveal information hidden in the frequency components of the image. For example, in the paper entitled "Airborne Hyperspectral Image Acquisition with Digital CCD Video Camera", Chengye Mao, Mike Seal, and Gerald Heitschmidt describe an airborne scanning system in which a linear variable filter ("LVF") is placed at the focal plane of a front objective lens, and, as an aircraft transports the scanner over the groundbased target, the linear variable filter separates frequency components of the image that passes by the front objective lens onto a CCD array within a camera. Unlike the present invention, the linear variable filter and CCD array are fixed with respect to the front objective lens, and the scanner must reside on a mobile platform and move past the target image in order to accomplish the scanning of the image.
It is therefore desirable to have an improved image scanner that need not reside on a mobile platform that moves relative to a target image in order to accomplish scanning of that target image, and it is further desirable that such an improved image scanner provide an imaging spectrograph of the scanned image.